The present invention relates to a testing master block so called an interim testing artifact for inspection or correction of the accuracy of a measuring apparatus such as a three dimensional measuring machine so called a coordinate measuring machine.
In the past, for the measurement of the dimensions of machine parts such as automobile engines or transmission cases, the measuring apparatus such as coordinate measuring machines, which measure dimensions by bringing the front end of a probe into contact with a measured object set on a measurement table (bed), have been used generally.
This type of measuring apparatus is maintained in accuracy of measurement by using a measurement master finished to a high accuracy to periodically inspect the accuracy or correct measurement error.
The measurement master is provided with a reference measurement plane to which a probe of the measuring apparatus may be brought into contact. By comparing the actually measured data of the reference measurement plane obtained by the measuring apparatus with a reference value, it is possible to inspect or correct the accuracy of the measuring apparatus.
As this type of measurement master proposed in the past, there is for example the measurement master disclosed in Japanese Unexamined Patent Publication (Kokai) No. 11-44527. Measurement hole members are provided respectively at the four corners of each of the top surfaces, one of the side surfaces and the front surface of a cubic hollow box made of cast iron.
Each of these reference hole members is shaped as a cylinder provided with a flange at one end and is bolted to the box with the flange. Further, the inner surface of the cylindrical portion is shaped as a circular hole finished to a high accuracy and forms a reference hole for measurement.
Further, in the master measuring apparatus disclosed-in Japanese Unexamined Patent Publication (Kokai) No. 4-160301, rods formed of a glass material with a coefficient of linear expansion of a value of about 0 are assembled into a grid and fastened to the outside of a cube-shaped or box-shaped hollow support block comprised of a low expansion material. The two end surfaces of the rods form the reference measurement planes, and at least three balls formed by a glass material etc. for setting reference coordinates are attached to the top surface of the support block.
In the inspection master disclosed in the above mentioned Japanese Unexamined Patent Publication (Kokai) No. 11-44527, since the reference hole members are attached to a hollow box made of cast iron, if a portion of the cast iron box expands or contracts due to a change of the ambient temperature, the distance or angle between the reference hole members changes slightly and it will be caused some defects on the inspection accuracy.
Further, in the master measuring apparatus disclosed in Japanese Unexamined Patent Publication (Kokai) No. 4-160301, by using glass material having a linear expansion coefficient of a value of about 0 for rods having two end surfaces as reference measurement planes or balls for setting the coordinates, it is being attempted that the inspection accuracy is improved by holding minimum expansion or contraction of the rods or balls themselves due to a change of the ambient temperature.
However, since the rods or balls are supported by a cast iron box, there are some problems that changes in the dimensions of the parts or warping of the shape of the box due to temperature changes of the box gives a bad influence on the inspection accuracy, the structure becomes complicated and the cost of manufacturing becomes higher.
An objective of the present invention is to provide a testing master block and manufacturing method of the same able to solve the above problems in the prior art and obtain high inspection accuracy by eliminating, as much as possible the effects due to changes in ambient temperature.
To achieve the above objective, the first aspect of the testing master block of the present invention is characterized by being provided with a hollow box-shaped block body with at least a top surface and four side surfaces comprised of quartz glass or single crystal quartz rectangular plates and a plurality of reference members each fastened by insertion to a plurality of mounting holes formed in the top surface and side surfaces of the block body and each having a reference measurement plane to which the front end of a probe of a measuring apparatus may be brought into contact.
Note that the term xe2x80x9crectangularxe2x80x9d as used in this specification includes xe2x80x9csquarexe2x80x9d and the term xe2x80x9cbox-shapedxe2x80x9d includes a xe2x80x9ccubexe2x80x9d.
The second aspect of the testing master block of the present invention is characterized by being provided with a hollow cylindrical block body comprised of a side surface of a quartz glass or single crystal quartz cylindrical tube and at least a top surface of a quartz glass or single crystal quartz disk and a plurality of reference members each fastened by insertion to a plurality of mounting holes formed in the top surface and side surface of the block body and each having a reference measurement plane to which the front end of a probe of a measuring apparatus may be brought into contact.
The third aspect of the testing master block of the present invention is characterized by being provided with a block body having at least a top surface and side surfaces and fabricated by being cut out from a single piece of quartz glass or single crystal quartz and a plurality of reference members each fastened by insertion to a plurality of mounting holes formed in the top surface and side surface of the block body and each having a reference measurement plane to which the front end of a probe of a measuring apparatus may be brought into contact.
In the first to third aspects of the testing master block, a reference member comprised of a ceramic ball with a surface serving as a reference measurement plane and a bushing holding the ceramic ball and fastened by insertion into a mounting hole of the block body may be used.
The first aspect of a manufacturing method of a testing master block of the present invention is characterized by comprising a first step of forming mounting holes at predetermined positions of rectangular plates comprised of quartz glass or single crystal quartz, a second step of forming at least a top surface and four side surfaces of a hollow box-shaped block body by joining a plurality of quartz glass or single crystal quartz rectangular plates so that the rectangular plates formed with the mounting holes in the previous step are positioned at least atone of the four side surfaces and the top surface, and a third step of fastening reference members to which the front end of a probe of a measuring apparatus may be brought into contact by insertion into the mounting holes after the second step.
The second aspect of the manufacturing method of a testing master block of the present invention is characterized by comprising a first step of forming mounting holes at predetermined positions of a quartz glass or single crystal quartz disk and a quartz glass or single crystal quartz cylindrical tube, a second step of forming a hollow cylindrical block body by joining a disk formed with mounting holes at the previous step to at least the top surface of the cylindrical tube, and a third step of fastening reference members to which the front end of a probe of a measuring apparatus may be brought into contact by insertion into the mounting holes after the second step.
A third aspect of the manufacturing method of a testing master block of the present invention is characterized by comprising a first step of cutting out a block body having at least a top surface and side surfaces from a single piece of quartz glass or single crystal quartz, a second step of forming mounting holes at predetermined positions of the top surface and side surfaces of the block body formed at the first step, and a third step of fastening reference members to which a front end of a probe of a measuring apparatus may be brought into contact by insertion into the mounting holes after the second step.
In the first to third aspects of the manufacturing method of a testing master block, the reference members after the third step may be finished into reference measurement planes to which a front end of a probe of a measuring apparatus may be brought into contact.
In the testing master block of the present invention (hereinafter referred to as the xe2x80x9cmaster blockxe2x80x9d), a plurality of reference members formed by a material with a small coefficient of linear expansion such as nonshrinking steel are attached to a block body made of quartz glass or single crystal quartz and reference measurement planes to which a probe of a measuring apparatus may be brought into contact are formed at these reference members.
The block body may be formed using rectangular plates made of quartz glass or single crystal quartz for at least the top surface and the four side surfaces and joining these plates into a hollow box or may be formed using a cylindrical tube and a disk made of quartz glass or single crystal quartz for the side surfaces and at least the top surface and joining these cylindrical tube and disk into a hollow cylinder.
Note that a commercially available instantaneous adhesive is suitable for joining the rectangular plates or the disk and the cylindrical tube.
Further, these reference members are fastened by insertion into mounting holes formed in the rectangular plates or the disk and cylindrical tube by a jig borer or other machine tool in advance before the assembly of the block body.
Further, the block body may be fabricated by being cut out into a block shape or tubular shape from a single piece of quartz glass or single crystal quartz using a diamond tool etc.
After the outer shape of the block body is cut out, mounting holes for insertion of the reference members are formed in the top surface and side surfaces of the block body by a jig borer etc.
Note that the block body cut out from the single material is preferably a hollow shape having a cavity with an open bottom in order to reduce its weight.
On the other hand, these reference members may be fastened by screws or other fastening means to the block body, but at this time, it is preferable to adhere the reference members to the mounting holes by applying an adhesive between the peripheral edges of the mounting holes and the reference members so that the fastening positions of the reference members do not shift.
Further, it is possible to affix the reference members to the mounting holes of the block body by just an adhesive without using screws or other fastening means.
Further, by finishing the reference measurement planes after affixing the reference members to the block body, it is possible to enhance the accuracy of the mounting angles or mounting positions of the reference measurement planes.
Note that the reference members may also be comprised using the surfaces of ceramic balls finished to a high accuracy as the reference measurement planes.
A quartz glass or single crystal quartz material has an extremely small coefficient of linear expansion, so the distance between the reference measurement planes of the reference members attached to the block body and the orientation of the reference measurement planes are almost completely free of the effect of changes in the ambient temperature and a high accuracy can be maintained.